types.hh

/*
 * Copyright (C) 2014 ScyllaDB
 */

/*
 * This file is part of Scylla.
 *
 * Scylla is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Scylla is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
 */

#pragma once

#include <experimental/optional>
#include <boost/functional/hash.hpp>
#include <iosfwd>
#include "data/cell.hh"
#include <sstream>

#include "core/sstring.hh"
#include "core/shared_ptr.hh"
#include "utils/UUID.hh"
#include "net/byteorder.hh"
#include "db_clock.hh"
#include "bytes.hh"
#include "log.hh"
#include "atomic_cell.hh"
#include "cql_serialization_format.hh"
#include "tombstone.hh"
#include "to_string.hh"
#include "duration.hh"
#include "marshal_exception.hh"
#include <boost/range/adaptor/transformed.hpp>
#include <boost/range/algorithm/for_each.hpp>
#include <boost/range/numeric.hpp>
#include <boost/range/combine.hpp>
#include "net/ip.hh"
#include <seastar/net/inet_address.hh>
#include "util/backtrace.hh"
#include "hashing.hh"
#include <boost/multiprecision/cpp_int.hpp>  // FIXME: remove somehow
#include "stdx.hh"
#include "utils/fragmented_temporary_buffer.hh"

class tuple_type_impl;
class big_decimal;

namespace Json {
class Value;
}

namespace cql3 {

class cql3_type;
class column_specification;
shared_ptr<cql3_type> make_cql3_tuple_type(shared_ptr<const tuple_type_impl> t);

}

// Specifies position in a lexicographically ordered sequence
// relative to some value.
//
// For example, if used with a value "bc" with lexicographical ordering on strings,
// each enum value represents the following positions in an example sequence:
//
//   aa
//   aaa
//   b
//   ba
// --> before_all_prefixed
//   bc
// --> before_all_strictly_prefixed
//   bca
//   bcd
// --> after_all_prefixed
//   bd
//   bda
//   c
//   ca
//
enum class lexicographical_relation : int8_t {
    before_all_prefixed,
    before_all_strictly_prefixed,
    after_all_prefixed
};

// Like std::lexicographical_compare but injects values from shared sequence (types) to the comparator
// Compare is an abstract_type-aware less comparator, which takes the type as first argument.
template <typename TypesIterator, typename InputIt1, typename InputIt2, typename Compare>
bool lexicographical_compare(TypesIterator types, InputIt1 first1, InputIt1 last1,
        InputIt2 first2, InputIt2 last2, Compare comp) {
    while (first1 != last1 && first2 != last2) {
        if (comp(*types, *first1, *first2)) {
            return true;
        }
        if (comp(*types, *first2, *first1)) {
            return false;
        }
        ++first1;
        ++first2;
        ++types;
    }
    return (first1 == last1) && (first2 != last2);
}

// Like std::lexicographical_compare but injects values from shared sequence
// (types) to the comparator. Compare is an abstract_type-aware trichotomic
// comparator, which takes the type as first argument.
//
// A trichotomic comparator returns an integer which is less, equal or greater
// than zero when the first value is respectively smaller, equal or greater
// than the second value.
template <typename TypesIterator, typename InputIt1, typename InputIt2, typename Compare>
int lexicographical_tri_compare(TypesIterator types_first, TypesIterator types_last,
        InputIt1 first1, InputIt1 last1,
        InputIt2 first2, InputIt2 last2,
        Compare comp,
        lexicographical_relation relation1 = lexicographical_relation::before_all_strictly_prefixed,
        lexicographical_relation relation2 = lexicographical_relation::before_all_strictly_prefixed) {
    while (types_first != types_last && first1 != last1 && first2 != last2) {
        auto c = comp(*types_first, *first1, *first2);
        if (c) {
            return c;
        }
        ++first1;
        ++first2;
        ++types_first;
    }
    bool e1 = first1 == last1;
    bool e2 = first2 == last2;
    if (e1 && e2) {
        return static_cast<int>(relation1) - static_cast<int>(relation2);
    }
    if (e2) {
        return relation2 == lexicographical_relation::after_all_prefixed ? -1 : 1;
    } else if (e1) {
        return relation1 == lexicographical_relation::after_all_prefixed ? 1 : -1;
    } else {
        return 0;
    }
}

// Trichotomic version of std::lexicographical_compare()
//
// Returns an integer which is less, equal or greater than zero when the first value
// is respectively smaller, equal or greater than the second value.
template <typename InputIt1, typename InputIt2, typename Compare>
int lexicographical_tri_compare(InputIt1 first1, InputIt1 last1,
        InputIt2 first2, InputIt2 last2,
        Compare comp,
        lexicographical_relation relation1 = lexicographical_relation::before_all_strictly_prefixed,
        lexicographical_relation relation2 = lexicographical_relation::before_all_strictly_prefixed) {
    while (first1 != last1 && first2 != last2) {
        auto c = comp(*first1, *first2);
        if (c) {
            return c;
        }
        ++first1;
        ++first2;
    }
    bool e1 = first1 == last1;
    bool e2 = first2 == last2;
    if (e1 == e2) {
        return static_cast<int>(relation1) - static_cast<int>(relation2);
    }
    if (e2) {
        return relation2 == lexicographical_relation::after_all_prefixed ? -1 : 1;
    } else {
        return relation1 == lexicographical_relation::after_all_prefixed ? 1 : -1;
    }
}

// A trichotomic comparator for prefix equality total ordering.
// In this ordering, two sequences are equal iff any of them is a prefix
// of the another. Otherwise, lexicographical ordering determines the order.
//
// 'comp' is an abstract_type-aware trichotomic comparator, which takes the
// type as first argument.
//
template <typename TypesIterator, typename InputIt1, typename InputIt2, typename Compare>
int prefix_equality_tri_compare(TypesIterator types, InputIt1 first1, InputIt1 last1,
        InputIt2 first2, InputIt2 last2, Compare comp) {
    while (first1 != last1 && first2 != last2) {
        auto c = comp(*types, *first1, *first2);
        if (c) {
            return c;
        }
        ++first1;
        ++first2;
        ++types;
    }
    return 0;
}

// Returns true iff the second sequence is a prefix of the first sequence
// Equality is an abstract_type-aware equality checker which takes the type as first argument.
template <typename TypesIterator, typename InputIt1, typename InputIt2, typename Equality>
bool is_prefixed_by(TypesIterator types, InputIt1 first1, InputIt1 last1,
        InputIt2 first2, InputIt2 last2, Equality equality) {
    while (first1 != last1 && first2 != last2) {
        if (!equality(*types, *first1, *first2)) {
            return false;
        }
        ++first1;
        ++first2;
        ++types;
    }
    return first2 == last2;
}

struct runtime_exception : public std::exception {
    sstring _why;
public:
    runtime_exception(sstring why) : _why(sstring("runtime error: ") + why) {}
    virtual const char* what() const noexcept override { return _why.c_str(); }
};

struct empty_t {};

class empty_value_exception : public std::exception {
public:
    virtual const char* what() const noexcept override {
        return "Unexpected empty value";
    }
};

// Cassandra has a notion of empty values even for scalars (i.e. int).  This is
// distinct from NULL which means deleted or never set.  It is serialized
// as a zero-length byte array (whereas NULL is serialized as a negative-length
// byte array).
template <typename T>
class emptyable {
    // We don't use optional<>, to avoid lots of ifs during the copy and move constructors
    static_assert(std::is_default_constructible<T>::value, "must be default constructible");
    bool _is_empty = false;
    T _value;
public:
    // default-constructor defaults to a non-empty value, since empty is the
    // exception rather than the rule
    emptyable() : _value{} {}
    emptyable(const T& x) : _value(x) {}
    emptyable(T&& x) : _value(std::move(x)) {}
    emptyable(empty_t) : _is_empty(true) {}
    template <typename... U>
    emptyable(U&&... args) : _value(std::forward<U>(args)...) {}
    bool empty() const { return _is_empty; }
    operator const T& () const { verify(); return _value; }
    operator T&& () && { verify(); return std::move(_value); }
    const T& get() const & { verify(); return _value; }
    T&& get() && { verify(); return std::move(_value); }
private:
    void verify() const {
        if (_is_empty) {
            throw empty_value_exception();
        }
    }
};

template <typename T>
inline
bool
operator==(const emptyable<T>& me1, const emptyable<T>& me2) {
    if (me1.empty() && me2.empty()) {
        return true;
    }
    if (me1.empty() != me2.empty()) {
        return false;
    }
    return me1.get() == me2.get();
}

template <typename T>
inline
bool
operator<(const emptyable<T>& me1, const emptyable<T>& me2) {
    if (me1.empty()) {
        if (me2.empty()) {
            return false;
        } else {
            return true;
        }
    }
    if (me2.empty()) {
        return false;
    } else {
        return me1.get() < me2.get();
    }
}

// Checks whether T::empty() const exists and returns bool
template <typename T>
class has_empty {
    template <typename X>
    constexpr static auto check(const X* x) -> std::enable_if_t<std::is_same<bool, decltype(x->empty())>::value, bool> {
        return true;
    }
    template <typename X>
    constexpr static auto check(...) -> bool {
        return false;
    }
public:
    constexpr static bool value = check<T>(nullptr);
};

template <typename T>
using maybe_empty =
        std::conditional_t<has_empty<T>::value, T, emptyable<T>>;

class abstract_type;
class data_value;

struct simple_date_native_type {
    using primary_type = uint32_t;
    primary_type days;
};

struct timestamp_native_type {
    using primary_type = db_clock::time_point;
    primary_type tp;
};

struct time_native_type {
    using primary_type = int64_t;
    primary_type nanoseconds;
};

struct timeuuid_native_type {
    using primary_type = utils::UUID;
    primary_type uuid;
};

using data_type = shared_ptr<const abstract_type>;

template <typename T>
const T& value_cast(const data_value& value);

template <typename T>
T&& value_cast(data_value&& value);

class data_value {
    void* _value;  // FIXME: use "small value optimization" for small types
    data_type _type;
private:
    data_value(void* value, data_type type) : _value(value), _type(std::move(type)) {}
    template <typename T>
    static data_value make_new(data_type type, T&& value);
public:
    ~data_value();
    data_value(const data_value&);
    data_value(data_value&& x) noexcept : _value(x._value), _type(std::move(x._type)) {
        x._value = nullptr;
    }
    // common conversions from C++ types to database types
    // note: somewhat dangerous, consider a factory function instead
    explicit data_value(bytes);
    data_value(sstring);
    data_value(const char*);
    data_value(bool);
    data_value(int8_t);
    data_value(int16_t);
    data_value(int32_t);
    data_value(int64_t);
    data_value(utils::UUID);
    data_value(float);
    data_value(double);
    data_value(net::ipv4_address);
    data_value(seastar::net::inet_address);
    data_value(simple_date_native_type);
    data_value(timestamp_native_type);
    data_value(time_native_type);
    data_value(timeuuid_native_type);
    data_value(db_clock::time_point);
    data_value(boost::multiprecision::cpp_int);
    data_value(big_decimal);
    data_value(cql_duration);
    explicit data_value(std::experimental::optional<bytes>);
    template <typename NativeType>
    data_value(std::experimental::optional<NativeType>);
    template <typename NativeType>
    data_value(const std::unordered_set<NativeType>&);

    data_value& operator=(const data_value&);
    data_value& operator=(data_value&&);
    const data_type& type() const {
        return _type;
    }
    bool is_null() const {   // may return false negatives for strings etc.
        return !_value;
    }
    size_t serialized_size() const;
    void serialize(bytes::iterator& out) const;
    bytes serialize() const;
    friend inline bool operator==(const data_value& x, const data_value& y);
    friend inline bool operator!=(const data_value& x, const data_value& y);
    friend class abstract_type;
    static data_value make_null(data_type type) {
        return data_value(nullptr, std::move(type));
    }
    template <typename T>
    static data_value make(data_type type, std::unique_ptr<T> value) {
        return data_value(value.release(), std::move(type));
    }
    friend class empty_type_impl;
    template <typename T> friend const T& value_cast(const data_value&);
    template <typename T> friend T&& value_cast(data_value&&);
    friend std::ostream& operator<<(std::ostream&, const data_value&);
    friend data_value make_tuple_value(data_type, maybe_empty<std::vector<data_value>>);
    friend data_value make_set_value(data_type, maybe_empty<std::vector<data_value>>);
    friend data_value make_list_value(data_type, maybe_empty<std::vector<data_value>>);
    friend data_value make_map_value(data_type, maybe_empty<std::vector<std::pair<data_value, data_value>>>);
    friend data_value make_user_value(data_type, std::vector<data_value>);
};

class serialized_compare;
class serialized_tri_compare;
class user_type_impl;

// Unsafe to access across shards unless otherwise noted.
class abstract_type : public enable_shared_from_this<abstract_type> {
    sstring _name;
    std::optional<uint32_t> _value_length_if_fixed;
    data::type_imr_descriptor _imr_state;
public:
    abstract_type(sstring name, std::optional<uint32_t> value_length_if_fixed, data::type_info ti)
        : _name(name), _value_length_if_fixed(std::move(value_length_if_fixed)), _imr_state(ti) {}
    virtual ~abstract_type() {}
    const data::type_imr_descriptor& imr_state() const { return _imr_state; }
    virtual void serialize(const void* value, bytes::iterator& out) const = 0;
    void serialize(const data_value& value, bytes::iterator& out) const {
        return serialize(get_value_ptr(value), out);
    }
    virtual size_t serialized_size(const void* value) const = 0;
    virtual bool less(bytes_view v1, bytes_view v2) const = 0;
    // returns a callable that can be called with two byte_views, and calls this->less() on them.
    serialized_compare as_less_comparator() const ;
    serialized_tri_compare as_tri_comparator() const ;
    static data_type parse_type(const sstring& name);
    virtual size_t hash(bytes_view v) const = 0;
    virtual bool equal(bytes_view v1, bytes_view v2) const {
        if (is_byte_order_equal()) {
            return compare_unsigned(v1, v2) == 0;
        }
        return compare(v1, v2) == 0;
    }
    virtual int32_t compare(bytes_view v1, bytes_view v2) const {
        if (less(v1, v2)) {
            return -1;
        } else if (less(v2, v1)) {
            return 1;
        } else {
            return 0;
        }
    }
    virtual data_value deserialize(bytes_view v) const = 0;
    data_value deserialize_value(bytes_view v) const {
        return deserialize(v);
    };
    virtual void validate(bytes_view v) const {
        // FIXME
    }
    virtual void validate(const fragmented_temporary_buffer::view& view) const {
        with_linearized(view, [this] (bytes_view bv) {
            validate(bv);
        });
    }
    virtual void validate_collection_member(bytes_view v, const bytes& collection_name) const {
        validate(v);
    }
    virtual bool is_compatible_with(const abstract_type& previous) const {
        return equals(previous);
    }
    /*
     * Types which are wrappers over other types should override this.
     * For example the reversed_type returns the type it is reversing.
     */
    virtual shared_ptr<const abstract_type> underlying_type() const {
        return shared_from_this();
    }
    /**
     * Returns true if values of the other AbstractType can be read and "reasonably" interpreted by the this
     * AbstractType. Note that this is a weaker version of isCompatibleWith, as it does not require that both type
     * compare values the same way.
     *
     * The restriction on the other type being "reasonably" interpreted is to prevent, for example, IntegerType from
     * being compatible with all other types.  Even though any byte string is a valid IntegerType value, it doesn't
     * necessarily make sense to interpret a UUID or a UTF8 string as an integer.
     *
     * Note that a type should be compatible with at least itself.
     */
    bool is_value_compatible_with(const abstract_type& other) const {
        return is_value_compatible_with_internal(*other.underlying_type());
    }
    bool equals(const shared_ptr<const abstract_type>& other) const {
        return equals(*other);
    }
    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const = 0;
    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const = 0;
    virtual bool references_duration() const {
        return false;
    }
    std::optional<uint32_t> value_length_if_fixed() const {
        return _value_length_if_fixed;
    }
protected:
    virtual bool equals(const abstract_type& other) const {
        return this == &other;
    }
    /**
     * Needed to handle ReversedType in value-compatibility checks.  Subclasses should implement this instead of
     * is_value_compatible_with().
     */
    virtual bool is_value_compatible_with_internal(const abstract_type& other) const {
        return is_compatible_with(other);
    }
public:
    bytes decompose(const data_value& value) const {
        if (!value._value) {
            return {};
        }
        bytes b(bytes::initialized_later(), serialized_size(value._value));
        auto i = b.begin();
        serialize(value._value, i);
        return b;
    }
    // Safe to call across shards
    const sstring& name() const {
        return _name;
    }
    virtual bool is_byte_order_comparable() const {
        return false;
    }

    /**
     * When returns true then equal values have the same byte representation and if byte
     * representation is different, the values are not equal.
     *
     * When returns false, nothing can be inferred.
     */
    virtual bool is_byte_order_equal() const {
        // If we're byte order comparable, then we must also be byte order equal.
        return is_byte_order_comparable();
    }
    virtual sstring get_string(const bytes& b) const {
        validate(b);
        return to_string(b);
    }
    virtual sstring to_string(const bytes& b) const = 0;
    virtual bytes from_string(sstring_view text) const = 0;
    virtual sstring to_json_string(const bytes& b) const = 0;
    sstring to_json_string(const bytes_opt& b) const {
        return b ? to_json_string(*b) : "null";
    }
    virtual bytes from_json_object(const Json::Value& value, cql_serialization_format sf) const = 0;
    virtual bool is_counter() const { return false; }
    virtual bool is_collection() const { return false; }
    virtual bool is_multi_cell() const { return false; }
    virtual bool is_atomic() const { return !is_multi_cell(); }
    virtual bool is_reversed() const { return false; }
    virtual bool is_tuple() const { return false; }
    virtual bool is_user_type() const { return false; }
    virtual ::shared_ptr<cql3::cql3_type> as_cql3_type() const = 0;
    virtual shared_ptr<const abstract_type> freeze() const { return shared_from_this(); }
    friend class list_type_impl;
protected:
    // native_value_* methods are virualized versions of native_type's
    // sizeof/alignof/copy-ctor/move-ctor etc.
    virtual size_t native_value_size() const = 0;
    virtual size_t native_value_alignment() const = 0;
    virtual void native_value_copy(const void* from, void* to) const = 0;
    virtual void native_value_move(void* from, void* to) const = 0;
    virtual void* native_value_clone(const void* from) const = 0;
    virtual void native_value_destroy(void* object) const = 0;
    virtual void native_value_delete(void* object) const = 0;
    virtual const std::type_info& native_typeid() const = 0;
    // abstract_type is a friend of data_value, but derived classes are not.
    static const void* get_value_ptr(const data_value& v) {
        return v._value;
    }
    friend void write_collection_value(bytes::iterator& out, cql_serialization_format sf, data_type type, const data_value& value);
    friend class tuple_type_impl;
    friend class data_value;
    friend class reversed_type_impl;
    template <typename T> friend const T& value_cast(const data_value& value);
    template <typename T> friend T&& value_cast(data_value&& value);
    friend bool operator==(const abstract_type& x, const abstract_type& y);
    static sstring quote_json_string(const sstring& s);
};

inline bool operator==(const abstract_type& x, const abstract_type& y)
{
     return x.equals(y);
}

inline
size_t
data_value::serialized_size() const {
    return _type->serialized_size(_value);
}


inline
void
data_value::serialize(bytes::iterator& out) const {
    return _type->serialize(_value, out);
}

inline
bytes
data_value::serialize() const {
    if (!_value) {
        return {};
    }
    bytes b(bytes::initialized_later(), serialized_size());
    auto i = b.begin();
    serialize(i);
    return b;
}

template <typename T>
inline
data_value
data_value::make_new(data_type type, T&& v) {
    maybe_empty<std::remove_reference_t<T>> value(std::forward<T>(v));
    return data_value(type->native_value_clone(&value), type);
}

template <typename T>
const T& value_cast(const data_value& value) {
    if (typeid(maybe_empty<T>) != value.type()->native_typeid()) {
        throw std::bad_cast();
    }
    if (value.is_null()) {
        throw std::runtime_error("value is null");
    }
    return *reinterpret_cast<maybe_empty<T>*>(value._value);
}

template <typename T>
T&& value_cast(data_value&& value) {
    if (typeid(maybe_empty<T>) != value.type()->native_typeid()) {
        throw std::bad_cast();
    }
    if (value.is_null()) {
        throw std::runtime_error("value is null");
    }
    return std::move(*reinterpret_cast<maybe_empty<T>*>(value._value));
}

// CRTP: implements translation between a native_type (C++ type) to abstract_type
// AbstractType is parametrized because we want a
//    abstract_type -> collection_type_impl -> map_type
// type hierarchy, and native_type is only known at the last step.
template <typename NativeType, typename AbstractType = abstract_type>
class concrete_type : public AbstractType {
public:
    using native_type = maybe_empty<NativeType>;
    using AbstractType::AbstractType;
protected:
    virtual size_t native_value_size() const override {
        return sizeof(native_type);
    }
    virtual size_t native_value_alignment() const override {
        return alignof(native_type);
    }
    virtual void native_value_copy(const void* from, void* to) const override {
        new (to) native_type(*reinterpret_cast<const native_type*>(from));
    }
    virtual void native_value_move(void* from, void* to) const override {
        new (to) native_type(std::move(*reinterpret_cast<native_type*>(from)));
    }
    virtual void native_value_destroy(void* object) const override {
        reinterpret_cast<native_type*>(object)->~native_type();
    }
    virtual void native_value_delete(void* object) const override {
        delete reinterpret_cast<native_type*>(object);
    }
    virtual void* native_value_clone(const void* object) const override {
        return new native_type(*reinterpret_cast<const native_type*>(object));
    }
    virtual const std::type_info& native_typeid() const override {
        return typeid(native_type);
    }
    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const override {
        return false;
    }
    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const override {
        return std::experimental::nullopt;
    }
protected:
    data_value make_value(std::unique_ptr<native_type> value) const {
        return data_value::make(this->shared_from_this(), std::move(value));
    }
    data_value make_value(native_type value) const {
        return make_value(std::make_unique<native_type>(std::move(value)));
    }
    data_value make_null() const {
        return data_value::make_null(this->shared_from_this());
    }
    data_value make_empty() const {
        return make_value(native_type(empty_t()));
    }
    const native_type& from_value(const void* v) const {
        return *reinterpret_cast<const native_type*>(v);
    }
    const native_type& from_value(const data_value& v) const {
        return this->from_value(AbstractType::get_value_ptr(v));
    }
};

inline bool operator==(const data_value& x, const data_value& y)
{
     return x._type->equals(y._type) && x._type->equal(x._type->decompose(x), y._type->decompose(y));
}

inline bool operator!=(const data_value& x, const data_value& y)
{
    return !(x == y);
}

using bytes_view_opt = std::experimental::optional<bytes_view>;

static inline
bool optional_less_compare(data_type t, bytes_view_opt e1, bytes_view_opt e2) {
    if (bool(e1) != bool(e2)) {
        return bool(e2);
    }
    if (!e1) {
        return false;
    }
    return t->less(*e1, *e2);
}

static inline
bool optional_equal(data_type t, bytes_view_opt e1, bytes_view_opt e2) {
    if (bool(e1) != bool(e2)) {
        return false;
    }
    if (!e1) {
        return true;
    }
    return t->equal(*e1, *e2);
}

static inline
bool less_compare(data_type t, bytes_view e1, bytes_view e2) {
    return t->less(e1, e2);
}

static inline
int tri_compare(data_type t, bytes_view e1, bytes_view e2) {
    return t->compare(e1, e2);
}

inline
int
tri_compare_opt(data_type t, bytes_view_opt v1, bytes_view_opt v2) {
    if (!v1 || !v2) {
        return int(bool(v1)) - int(bool(v2));
    } else {
        return tri_compare(std::move(t), *v1, *v2);
    }
}

static inline
bool equal(data_type t, bytes_view e1, bytes_view e2) {
    return t->equal(e1, e2);
}

class row_tombstone;

class collection_type_impl : public abstract_type {
    static logging::logger _logger;
    static thread_local std::unordered_map<data_type, shared_ptr<cql3::cql3_type>> _cql3_type_cache;  // initialized on demand
public:
    static constexpr size_t max_elements = 65535;

    class kind {
        std::function<shared_ptr<cql3::column_specification> (shared_ptr<cql3::column_specification> collection, bool is_key)> _impl;
    public:
        kind(std::function<shared_ptr<cql3::column_specification> (shared_ptr<cql3::column_specification> collection, bool is_key)> impl)
            : _impl(std::move(impl)) {}
        shared_ptr<cql3::column_specification> make_collection_receiver(shared_ptr<cql3::column_specification> collection, bool is_key) const;
        static const kind map;
        static const kind set;
        static const kind list;
    };

    const kind& _kind;

protected:
    explicit collection_type_impl(sstring name, const kind& k)
            : abstract_type(std::move(name), {}, data::type_info::make_collection()), _kind(k) {}
    virtual sstring cql3_type_name() const = 0;
public:
    // representation of a collection mutation, key/value pairs, value is a mutation itself
    struct mutation {
        tombstone tomb;
        std::vector<std::pair<bytes, atomic_cell>> cells;
        // Expires cells based on query_time. Expires tombstones based on max_purgeable and gc_before.
        // Removes cells covered by tomb or this->tomb.
        bool compact_and_expire(row_tombstone tomb, gc_clock::time_point query_time,
            can_gc_fn&, gc_clock::time_point gc_before);
    };
    struct mutation_view {
        tombstone tomb;
        std::vector<std::pair<bytes_view, atomic_cell_view>> cells;
        mutation materialize(const collection_type_impl&) const;
    };
    virtual data_type name_comparator() const = 0;
    virtual data_type value_comparator() const = 0;
    shared_ptr<cql3::column_specification> make_collection_receiver(shared_ptr<cql3::column_specification> collection, bool is_key) const;
    virtual bool is_collection() const override { return true; }
    bool is_map() const { return &_kind == &kind::map; }
    bool is_set() const { return &_kind == &kind::set; }
    bool is_list() const { return &_kind == &kind::list; }
    std::vector<atomic_cell> enforce_limit(std::vector<atomic_cell>, int version) const;
    virtual std::vector<bytes> serialized_values(std::vector<atomic_cell> cells) const = 0;
    bytes serialize_for_native_protocol(std::vector<atomic_cell> cells, int version) const;
    virtual bool is_compatible_with(const abstract_type& previous) const override;
    virtual bool is_value_compatible_with_internal(const abstract_type& other) const override;
    virtual bool is_compatible_with_frozen(const collection_type_impl& previous) const = 0;
    virtual bool is_value_compatible_with_frozen(const collection_type_impl& previous) const = 0;
    virtual shared_ptr<cql3::cql3_type> as_cql3_type() const override;
    template <typename BytesViewIterator>
    static bytes pack(BytesViewIterator start, BytesViewIterator finish, int elements, cql_serialization_format sf);
    // requires linearized collection_mutation_view, lifetime
    mutation_view deserialize_mutation_form(bytes_view in) const;
    bool is_empty(collection_mutation_view in) const;
    bool is_any_live(collection_mutation_view in, tombstone tomb = tombstone(), gc_clock::time_point now = gc_clock::time_point::min()) const;
    api::timestamp_type last_update(collection_mutation_view in) const;
    virtual bytes to_value(mutation_view mut, cql_serialization_format sf) const = 0;
    bytes to_value(collection_mutation_view mut, cql_serialization_format sf) const;
    // FIXME: use iterators?
    collection_mutation serialize_mutation_form(const mutation& mut) const;
    collection_mutation serialize_mutation_form(mutation_view mut) const;
    collection_mutation serialize_mutation_form_only_live(mutation_view mut, gc_clock::time_point now) const;
    collection_mutation merge(collection_mutation_view a, collection_mutation_view b) const;
    collection_mutation difference(collection_mutation_view a, collection_mutation_view b) const;
    // Calls Func(atomic_cell_view) for each cell in this collection.
    // noexcept if Func doesn't throw.
    template<typename Func>
    void for_each_cell(collection_mutation_view c, Func&& func) const {
      c.data.with_linearized([&] (bytes_view c_bv) {
        auto m_view = deserialize_mutation_form(c_bv);
        for (auto&& c : m_view.cells) {
            func(std::move(c.second));
        }
      });
    }
    virtual void serialize(const void* value, bytes::iterator& out, cql_serialization_format sf) const = 0;
    virtual data_value deserialize(bytes_view v, cql_serialization_format sf) const = 0;
    data_value deserialize_value(bytes_view v, cql_serialization_format sf) const {
        return deserialize(v, sf);
    }
    bytes_opt reserialize(cql_serialization_format from, cql_serialization_format to, bytes_view_opt v) const;
};

using collection_type = shared_ptr<const collection_type_impl>;

template <typename... T>
struct simple_tuple_hash;

template <>
struct simple_tuple_hash<> {
    size_t operator()() const { return 0; }
};

template <typename Arg0, typename... Args >
struct simple_tuple_hash<std::vector<Arg0>, Args...> {
    size_t operator()(const std::vector<Arg0>& vec, const Args&... args) const {
        size_t h0 = 0;
        size_t h1;
        for (auto&& i : vec) {
            h1 = std::hash<Arg0>()(i);
            h0 = h0 ^ ((h1 << 7) | (h1 >> (std::numeric_limits<size_t>::digits - 7)));
        }
        h1 = simple_tuple_hash<Args...>()(args...);
        return h0 ^ ((h1 << 7) | (h1 >> (std::numeric_limits<size_t>::digits - 7)));
    }
};

template <typename Arg0, typename... Args>
struct simple_tuple_hash<Arg0, Args...> {
    size_t operator()(const Arg0& arg0, const Args&... args) const {
        size_t h0 = std::hash<Arg0>()(arg0);
        size_t h1 = simple_tuple_hash<Args...>()(args...);
        return h0 ^ ((h1 << 7) | (h1 >> (std::numeric_limits<size_t>::digits - 7)));
    }
};

template <typename InternedType, typename... BaseTypes>
class type_interning_helper {
    using key_type = std::tuple<BaseTypes...>;
    using value_type = shared_ptr<const InternedType>;
    struct hash_type {
        size_t operator()(const key_type& k) const {
            return apply(simple_tuple_hash<BaseTypes...>(), k);
        }
    };
    using map_type = std::unordered_map<key_type, value_type, hash_type>;
    static thread_local map_type _instances;
public:
    static shared_ptr<const InternedType> get_instance(BaseTypes... keys) {
        auto key = std::make_tuple(keys...);
        auto i = _instances.find(key);
        if (i == _instances.end()) {
            auto v = ::make_shared<InternedType>(std::move(keys)...);
            i = _instances.insert(std::make_pair(std::move(key), std::move(v))).first;
        }
        return i->second;
    }
};

template <typename InternedType, typename... BaseTypes>
thread_local typename type_interning_helper<InternedType, BaseTypes...>::map_type
    type_interning_helper<InternedType, BaseTypes...>::_instances;

class reversed_type_impl : public abstract_type {
    using intern = type_interning_helper<reversed_type_impl, data_type>;
    friend struct shared_ptr_make_helper<reversed_type_impl, true>;

    data_type _underlying_type;
    reversed_type_impl(data_type t)
        : abstract_type("org.apache.cassandra.db.marshal.ReversedType(" + t->name() + ")",
                        t->value_length_if_fixed(), t->imr_state().type_info())
        , _underlying_type(t)
    {}
protected:
    virtual bool is_value_compatible_with_internal(const abstract_type& other) const {
        return _underlying_type->is_value_compatible_with(*(other.underlying_type()));
    }
public:
    virtual int32_t compare(bytes_view v1, bytes_view v2) const override {
        return _underlying_type->compare(v2, v1);
    }
    virtual bool less(bytes_view v1, bytes_view v2) const override {
        return _underlying_type->less(v2, v1);
    }

    virtual bool equal(bytes_view v1, bytes_view v2) const override {
        return _underlying_type->equal(v1, v2);
    }

    virtual void validate(bytes_view v) const override {
        _underlying_type->validate(v);
    }

    virtual void validate_collection_member(bytes_view v, const bytes& collection_name) const  override {
        _underlying_type->validate_collection_member(v, collection_name);
    }

    virtual bool is_compatible_with(const abstract_type& previous) const override {
        if (previous.is_reversed()) {
            return _underlying_type->is_compatible_with(*previous.underlying_type());
        }
        return false;
    }

    virtual shared_ptr<const abstract_type> underlying_type() const override {
        return _underlying_type;
    }

    virtual bool is_byte_order_comparable() const override {
        return _underlying_type->is_byte_order_comparable();
    }
    virtual bool is_byte_order_equal() const override {
        return _underlying_type->is_byte_order_equal();
    }
    virtual size_t hash(bytes_view v) const override {
        return _underlying_type->hash(v);
    }
    virtual bool is_reversed() const override { return true; }
    virtual bool is_counter() const override {
        return _underlying_type->is_counter();
    }
    virtual bool is_collection() const override {
        return _underlying_type->is_collection();
    }
    virtual bool is_multi_cell() const override {
        return _underlying_type->is_multi_cell();
    }

    virtual void serialize(const void* value, bytes::iterator& out) const override {
        _underlying_type->serialize(value, out);
    }
    virtual size_t serialized_size(const void* value) const override {
        return _underlying_type->serialized_size(value);
    }
    virtual data_value deserialize(bytes_view v) const override {
        return _underlying_type->deserialize(v);
    }

    virtual sstring get_string(const bytes& b) const override {
        return _underlying_type->get_string(b);
    }
    virtual sstring to_string(const bytes& b) const override {
        return _underlying_type->to_string(b);
    }
    virtual sstring to_json_string(const bytes& b) const override {
        return _underlying_type->to_json_string(b);
    }
    virtual bytes from_json_object(const Json::Value& value, cql_serialization_format sf) const override {
        return _underlying_type->from_json_object(value, sf);
    }
    virtual bytes from_string(sstring_view s) const override {
        return _underlying_type->from_string(s);
    }

    virtual ::shared_ptr<cql3::cql3_type> as_cql3_type() const override {
        return _underlying_type->as_cql3_type();
    }

    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const override {
        return _underlying_type->references_user_type(keyspace, name);
    }

    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const override {
        return _underlying_type->update_user_type(updated);
    }

    static shared_ptr<const reversed_type_impl> get_instance(data_type type) {
        return intern::get_instance(std::move(type));
    }

protected:
    virtual size_t native_value_size() const override;
    virtual size_t native_value_alignment() const override;
    virtual void native_value_copy(const void* from, void* to) const override;
    virtual void native_value_move(void* from, void* to) const override;
    virtual void native_value_destroy(void* object) const override;
    virtual void* native_value_clone(const void* object) const override;
    virtual void native_value_delete(void* object) const override;
    virtual const std::type_info& native_typeid() const override;
};
using reversed_type = shared_ptr<const reversed_type_impl>;

template <typename NativeType>
using concrete_collection_type = concrete_type<NativeType, collection_type_impl>;

class map_type_impl final : public concrete_collection_type<std::vector<std::pair<data_value, data_value>>> {
    using map_type = shared_ptr<const map_type_impl>;
    using intern = type_interning_helper<map_type_impl, data_type, data_type, bool>;
    data_type _keys;
    data_type _values;
    data_type _key_value_pair_type;
    bool _is_multi_cell;
protected:
    virtual sstring cql3_type_name() const override;
public:
    static shared_ptr<const map_type_impl> get_instance(data_type keys, data_type values, bool is_multi_cell);
    map_type_impl(data_type keys, data_type values, bool is_multi_cell);
    data_type get_keys_type() const { return _keys; }
    data_type get_values_type() const { return _values; }
    virtual data_type name_comparator() const override { return _keys; }
    virtual data_type value_comparator() const override { return _values; }
    virtual bool is_multi_cell() const override { return _is_multi_cell; }
    virtual data_type freeze() const override;
    virtual bool is_compatible_with_frozen(const collection_type_impl& previous) const override;
    virtual bool is_value_compatible_with_frozen(const collection_type_impl& previous) const override;
    virtual bool less(bytes_view o1, bytes_view o2) const override;
    static int32_t compare_maps(data_type keys_comparator, data_type values_comparator,
                        bytes_view o1, bytes_view o2);
    virtual bool is_byte_order_comparable() const override { return false; }
    virtual void serialize(const void* value, bytes::iterator& out) const override;
    virtual void serialize(const void* value, bytes::iterator& out, cql_serialization_format sf) const override;
    virtual size_t serialized_size(const void* value) const;
    virtual data_value deserialize(bytes_view v) const override;
    virtual data_value deserialize(bytes_view v, cql_serialization_format sf) const override;
    virtual sstring to_string(const bytes& b) const override;
    virtual sstring to_json_string(const bytes& b) const override;
    virtual bytes from_json_object(const Json::Value& value, cql_serialization_format sf) const override;
    virtual size_t hash(bytes_view v) const override;
    virtual bytes from_string(sstring_view text) const override;
    virtual std::vector<bytes> serialized_values(std::vector<atomic_cell> cells) const override;
    static bytes serialize_partially_deserialized_form(const std::vector<std::pair<bytes_view, bytes_view>>& v,
            cql_serialization_format sf);
    virtual bytes to_value(mutation_view mut, cql_serialization_format sf) const override;
    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const override;
    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const override;
    virtual bool references_duration() const override;
};

using map_type = shared_ptr<const map_type_impl>;

data_value make_map_value(data_type tuple_type, map_type_impl::native_type value);

class set_type_impl final : public concrete_collection_type<std::vector<data_value>> {
    using set_type = shared_ptr<const set_type_impl>;
    using intern = type_interning_helper<set_type_impl, data_type, bool>;
    data_type _elements;
    bool _is_multi_cell;
protected:
    virtual sstring cql3_type_name() const override;
public:
    static set_type get_instance(data_type elements, bool is_multi_cell);
    set_type_impl(data_type elements, bool is_multi_cell);
    data_type get_elements_type() const { return _elements; }
    virtual data_type name_comparator() const override { return _elements; }
    virtual data_type value_comparator() const override;
    virtual bool is_multi_cell() const override { return _is_multi_cell; }
    virtual data_type freeze() const override;
    virtual bool is_compatible_with_frozen(const collection_type_impl& previous) const override;
    virtual bool is_value_compatible_with_frozen(const collection_type_impl& previous) const override;
    virtual bool less(bytes_view o1, bytes_view o2) const override;
    virtual bool is_byte_order_comparable() const override { return _elements->is_byte_order_comparable(); }
    virtual void serialize(const void* value, bytes::iterator& out) const override;
    virtual void serialize(const void* value, bytes::iterator& out, cql_serialization_format sf) const override;
    virtual size_t serialized_size(const void* value) const override;
    virtual data_value deserialize(bytes_view v) const override;
    virtual data_value deserialize(bytes_view v, cql_serialization_format sf) const override;
    virtual sstring to_string(const bytes& b) const override;
    virtual sstring to_json_string(const bytes& b) const override;
    virtual bytes from_json_object(const Json::Value& value, cql_serialization_format sf) const override;
    virtual size_t hash(bytes_view v) const override;
    virtual bytes from_string(sstring_view text) const override;
    virtual std::vector<bytes> serialized_values(std::vector<atomic_cell> cells) const override;
    virtual bytes to_value(mutation_view mut, cql_serialization_format sf) const override;
    bytes serialize_partially_deserialized_form(
            const std::vector<bytes_view>& v, cql_serialization_format sf) const;
    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const override;
    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const override;
    virtual bool references_duration() const override;
};

using set_type = shared_ptr<const set_type_impl>;

data_value make_set_value(data_type tuple_type, set_type_impl::native_type value);

class list_type_impl final : public concrete_collection_type<std::vector<data_value>> {
    using list_type = shared_ptr<const list_type_impl>;
    using intern = type_interning_helper<list_type_impl, data_type, bool>;
    data_type _elements;
    bool _is_multi_cell;
protected:
    virtual sstring cql3_type_name() const override;
public:
    static list_type get_instance(data_type elements, bool is_multi_cell);
    list_type_impl(data_type elements, bool is_multi_cell);
    data_type get_elements_type() const { return _elements; }
    virtual data_type name_comparator() const override;
    virtual data_type value_comparator() const override;
    virtual bool is_multi_cell() const override { return _is_multi_cell; }
    virtual data_type freeze() const override;
    virtual bool is_compatible_with_frozen(const collection_type_impl& previous) const override;
    virtual bool is_value_compatible_with_frozen(const collection_type_impl& previous) const override;
    virtual bool less(bytes_view o1, bytes_view o2) const override;
    // FIXME: origin doesn't override is_byte_order_comparable().  Why?
    virtual void serialize(const void* value, bytes::iterator& out) const override;
    virtual void serialize(const void* value, bytes::iterator& out, cql_serialization_format sf) const override;
    virtual size_t serialized_size(const void* value) const override;
    virtual data_value deserialize(bytes_view v) const override;
    virtual data_value deserialize(bytes_view v, cql_serialization_format sf) const override;
    virtual sstring to_string(const bytes& b) const override;
    virtual sstring to_json_string(const bytes& b) const override;
    virtual bytes from_json_object(const Json::Value& value, cql_serialization_format sf) const override;
    virtual size_t hash(bytes_view v) const override;
    virtual bytes from_string(sstring_view text) const override;
    virtual std::vector<bytes> serialized_values(std::vector<atomic_cell> cells) const override;
    virtual bytes to_value(mutation_view mut, cql_serialization_format sf) const override;
    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const override;
    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const override;
    virtual bool references_duration() const override;
};

using list_type = shared_ptr<const list_type_impl>;

data_value make_list_value(data_type type, list_type_impl::native_type value);

inline
size_t hash_value(const shared_ptr<const abstract_type>& x) {
    return std::hash<const abstract_type*>()(x.get());
}

template <typename Type>
shared_ptr<const abstract_type> data_type_for();

class serialized_compare {
    data_type _type;
public:
    serialized_compare(data_type type) : _type(type) {}
    bool operator()(const bytes& v1, const bytes& v2) const {
        return _type->less(v1, v2);
    }
};

inline
serialized_compare
abstract_type::as_less_comparator() const {
    return serialized_compare(shared_from_this());
}

class serialized_tri_compare {
    data_type _type;
public:
    serialized_tri_compare(data_type type) : _type(type) {}
    int operator()(const bytes_view& v1, const bytes_view& v2) const {
        return _type->compare(v1, v2);
    }
};

inline
serialized_tri_compare
abstract_type::as_tri_comparator() const {
    return serialized_tri_compare(shared_from_this());
}

using key_compare = serialized_compare;

// Remember to update type_codec in transport/server.cc and cql3/cql3_type.cc
extern thread_local const shared_ptr<const abstract_type> byte_type;
extern thread_local const shared_ptr<const abstract_type> short_type;
extern thread_local const shared_ptr<const abstract_type> int32_type;
extern thread_local const shared_ptr<const abstract_type> long_type;
extern thread_local const shared_ptr<const abstract_type> ascii_type;
extern thread_local const shared_ptr<const abstract_type> bytes_type;
extern thread_local const shared_ptr<const abstract_type> utf8_type;
extern thread_local const shared_ptr<const abstract_type> boolean_type;
extern thread_local const shared_ptr<const abstract_type> date_type;
extern thread_local const shared_ptr<const abstract_type> timeuuid_type;
extern thread_local const shared_ptr<const abstract_type> timestamp_type;
extern thread_local const shared_ptr<const abstract_type> simple_date_type;
extern thread_local const shared_ptr<const abstract_type> time_type;
extern thread_local const shared_ptr<const abstract_type> uuid_type;
extern thread_local const shared_ptr<const abstract_type> inet_addr_type;
extern thread_local const shared_ptr<const abstract_type> float_type;
extern thread_local const shared_ptr<const abstract_type> double_type;
extern thread_local const shared_ptr<const abstract_type> varint_type;
extern thread_local const shared_ptr<const abstract_type> decimal_type;
extern thread_local const shared_ptr<const abstract_type> counter_type;
extern thread_local const shared_ptr<const abstract_type> duration_type;
extern thread_local const data_type empty_type;

template <>
inline
shared_ptr<const abstract_type> data_type_for<int8_t>() {
    return byte_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<int16_t>() {
    return short_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<int32_t>() {
    return int32_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<int64_t>() {
    return long_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<sstring>() {
    return utf8_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<bytes>() {
    return bytes_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<utils::UUID>() {
    return uuid_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<db_clock::time_point>() {
    return date_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<simple_date_native_type>() {
    return simple_date_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<timestamp_native_type>() {
    return timestamp_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<time_native_type>() {
    return time_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<timeuuid_native_type>() {
    return timeuuid_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<net::inet_address>() {
    return inet_addr_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<bool>() {
    return boolean_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<float>() {
    return float_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<double>() {
    return double_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<boost::multiprecision::cpp_int>() {
    return varint_type;
}

template <>
inline
shared_ptr<const abstract_type> data_type_for<big_decimal>() {
    return decimal_type;
}

namespace std {

template <>
struct hash<shared_ptr<const abstract_type>> : boost::hash<shared_ptr<abstract_type>> {
};

}

// FIXME: make more explicit
inline
bytes
to_bytes(const char* x) {
    return bytes(reinterpret_cast<const int8_t*>(x), std::strlen(x));
}

// FIXME: make more explicit
inline
bytes
to_bytes(const std::string& x) {
    return bytes(reinterpret_cast<const int8_t*>(x.data()), x.size());
}

inline
bytes_view
to_bytes_view(const std::string& x) {
    return bytes_view(reinterpret_cast<const int8_t*>(x.data()), x.size());
}

inline
bytes
to_bytes(bytes_view x) {
    return bytes(x.begin(), x.size());
}

inline
bytes_opt
to_bytes_opt(bytes_view_opt bv) {
    if (bv) {
        return to_bytes(*bv);
    }
    return std::experimental::nullopt;
}

inline
bytes_view_opt
as_bytes_view_opt(const bytes_opt& bv) {
    if (bv) {
        return bytes_view{*bv};
    }
    return std::experimental::nullopt;
}

// FIXME: make more explicit
inline
bytes
to_bytes(const sstring& x) {
    return bytes(reinterpret_cast<const int8_t*>(x.c_str()), x.size());
}

inline
bytes_view
to_bytes_view(const sstring& x) {
    return bytes_view(reinterpret_cast<const int8_t*>(x.c_str()), x.size());
}

inline
bytes
to_bytes(const utils::UUID& uuid) {
    struct {
        uint64_t msb;
        uint64_t lsb;
    } tmp = { net::hton(uint64_t(uuid.get_most_significant_bits())),
        net::hton(uint64_t(uuid.get_least_significant_bits())) };
    return bytes(reinterpret_cast<int8_t*>(&tmp), 16);
}

// This follows java.util.Comparator
// FIXME: Choose a better place than database.hh
template <typename T>
struct comparator {
    comparator() = default;
    comparator(std::function<int32_t (T& v1, T& v2)> fn)
        : _compare_fn(std::move(fn))
    { }
    int32_t compare() { return _compare_fn(); }
private:
    std::function<int32_t (T& v1, T& v2)> _compare_fn;
};

inline bool
less_unsigned(bytes_view v1, bytes_view v2) {
    return compare_unsigned(v1, v2) < 0;
}

class serialized_hash {
private:
    data_type _type;
public:
    serialized_hash(data_type type) : _type(type) {}
    size_t operator()(const bytes& v) const {
        return _type->hash(v);
    }
};

class serialized_equal {
private:
    data_type _type;
public:
    serialized_equal(data_type type) : _type(type) {}
    bool operator()(const bytes& v1, const bytes& v2) const {
        return _type->equal(v1, v2);
    }
};

template<typename Type>
static inline
typename Type::value_type deserialize_value(Type& t, bytes_view v) {
    return t.deserialize_value(v);
}

template<typename Type, typename Value>
static inline
bytes serialize_value(Type& t, const Value& value) {
    bytes b(bytes::initialized_later(), t.serialized_size(value));
    auto i = b.begin();
    t.serialize_value(value, i);
    return b;
}

template<typename T>
T read_simple(bytes_view& v) {
    if (v.size() < sizeof(T)) {
        throw_with_backtrace<marshal_exception>(sprint("read_simple - not enough bytes (expected %d, got %d)", sizeof(T), v.size()));
    }
    auto p = v.begin();
    v.remove_prefix(sizeof(T));
    return net::ntoh(*reinterpret_cast<const net::packed<T>*>(p));
}

template<typename T>
T read_simple_exactly(bytes_view v) {
    if (v.size() != sizeof(T)) {
        throw_with_backtrace<marshal_exception>(sprint("read_simple_exactly - size mismatch (expected %d, got %d)", sizeof(T), v.size()));
    }
    auto p = v.begin();
    return net::ntoh(*reinterpret_cast<const net::packed<T>*>(p));
}

inline
bytes_view
read_simple_bytes(bytes_view& v, size_t n) {
    if (v.size() < n) {
        throw_with_backtrace<marshal_exception>(sprint("read_simple_bytes - not enough bytes (requested %d, got %d)", n, v.size()));
    }
    bytes_view ret(v.begin(), n);
    v.remove_prefix(n);
    return ret;
}

template<typename T>
std::experimental::optional<T> read_simple_opt(bytes_view& v) {
    if (v.empty()) {
        return {};
    }
    if (v.size() != sizeof(T)) {
        throw_with_backtrace<marshal_exception>(sprint("read_simple_opt - size mismatch (expected %d, got %d)", sizeof(T), v.size()));
    }
    auto p = v.begin();
    v.remove_prefix(sizeof(T));
    return { net::ntoh(*reinterpret_cast<const net::packed<T>*>(p)) };
}

inline sstring read_simple_short_string(bytes_view& v) {
    uint16_t len = read_simple<uint16_t>(v);
    if (v.size() < len) {
        throw_with_backtrace<marshal_exception>(sprint("read_simple_short_string - not enough bytes (%d)", v.size()));
    }
    sstring ret(sstring::initialized_later(), len);
    std::copy(v.begin(), v.begin() + len, ret.begin());
    v.remove_prefix(len);
    return ret;
}

size_t collection_size_len(cql_serialization_format sf);
size_t collection_value_len(cql_serialization_format sf);
void write_collection_size(bytes::iterator& out, int size, cql_serialization_format sf);
void write_collection_value(bytes::iterator& out, cql_serialization_format sf, bytes_view val_bytes);
void write_collection_value(bytes::iterator& out, cql_serialization_format sf, data_type type, const data_value& value);

template <typename BytesViewIterator>
bytes
collection_type_impl::pack(BytesViewIterator start, BytesViewIterator finish, int elements, cql_serialization_format sf) {
    size_t len = collection_size_len(sf);
    size_t psz = collection_value_len(sf);
    for (auto j = start; j != finish; j++) {
        len += j->size() + psz;
    }
    bytes out(bytes::initialized_later(), len);
    bytes::iterator i = out.begin();
    write_collection_size(i, elements, sf);
    while (start != finish) {
        write_collection_value(i, sf, *start++);
    }
    return out;
}

struct tuple_deserializing_iterator : public std::iterator<std::input_iterator_tag, const bytes_view_opt> {
    bytes_view _v;
    bytes_view_opt _current;
public:
    struct end_tag {};
    tuple_deserializing_iterator(bytes_view v) : _v(v) {
        parse();
    }
    tuple_deserializing_iterator(end_tag, bytes_view v) : _v(v) {
        _v.remove_prefix(_v.size());
    }
    static tuple_deserializing_iterator start(bytes_view v) {
        return tuple_deserializing_iterator(v);
    }
    static tuple_deserializing_iterator finish(bytes_view v) {
        return tuple_deserializing_iterator(end_tag(), v);
    }
    const bytes_view_opt& operator*() const {
        return _current;
    }
    const bytes_view_opt* operator->() const {
        return &_current;
    }
    tuple_deserializing_iterator& operator++() {
        skip();
        parse();
        return *this;
    }
    void operator++(int) {
        skip();
        parse();
    }
    bool operator==(const tuple_deserializing_iterator& x) const {
        return _v == x._v;
    }
    bool operator!=(const tuple_deserializing_iterator& x) const {
        return !operator==(x);
    }
private:
    void parse() {
        _current = std::experimental::nullopt;
        if (_v.empty()) {
            return;
        }
        // we don't consume _v, otherwise operator==
        // or the copy constructor immediately after
        // parse() yields the wrong results.
        auto tmp = _v;
        auto s = read_simple<int32_t>(tmp);
        if (s < 0) {
            return;
        }
        _current = read_simple_bytes(tmp, s);
    }
    void skip() {
        _v.remove_prefix(4 + (_current ? _current->size() : 0));
    }
};

class tuple_type_impl : public concrete_type<std::vector<data_value>> {
    using intern = type_interning_helper<tuple_type_impl, std::vector<data_type>>;
protected:
    std::vector<data_type> _types;
    static boost::iterator_range<tuple_deserializing_iterator> make_range(bytes_view v) {
        return { tuple_deserializing_iterator::start(v), tuple_deserializing_iterator::finish(v) };
    }
    tuple_type_impl(sstring name, std::vector<data_type> types);
public:
    tuple_type_impl(std::vector<data_type> types);
    static shared_ptr<const tuple_type_impl> get_instance(std::vector<data_type> types);
    data_type type(size_t i) const {
        return _types[i];
    }
    size_t size() const {
        return _types.size();
    }
    const std::vector<data_type>& all_types() const {
        return _types;
    }
    virtual int32_t compare(bytes_view v1, bytes_view v2) const override;
    virtual bool less(bytes_view v1, bytes_view v2) const override;
    virtual size_t serialized_size(const void* value) const override;
    virtual void serialize(const void* value, bytes::iterator& out) const override;
    virtual data_value deserialize(bytes_view v) const override;
    std::vector<bytes_view_opt> split(bytes_view v) const;
    template <typename RangeOf_bytes_opt>  // also accepts bytes_view_opt
    static bytes build_value(RangeOf_bytes_opt&& range) {
        auto item_size = [] (auto&& v) { return 4 + (v ? v->size() : 0); };
        auto size = boost::accumulate(range | boost::adaptors::transformed(item_size), 0);
        auto ret = bytes(bytes::initialized_later(), size);
        auto out = ret.begin();
        auto put = [&out] (auto&& v) {
            if (v) {
                write(out, int32_t(v->size()));
                out = std::copy(v->begin(), v->end(), out);
            } else {
                write(out, int32_t(-1));
            }
        };
        boost::range::for_each(range, put);
        return ret;
    }
    virtual size_t hash(bytes_view v) const override;
    virtual bytes from_string(sstring_view s) const override;
    virtual sstring to_string(const bytes& b) const override;
    virtual sstring to_json_string(const bytes& b) const override;
    virtual bytes from_json_object(const Json::Value& value, cql_serialization_format sf) const override;
    virtual bool equals(const abstract_type& other) const override;
    virtual bool is_compatible_with(const abstract_type& previous) const override;
    virtual bool is_value_compatible_with_internal(const abstract_type& previous) const override;
    virtual shared_ptr<cql3::cql3_type> as_cql3_type() const override;
    virtual bool is_tuple() const override { return true; }
    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const override;
    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const override;
    virtual bool references_duration() const override;
private:
    bool check_compatibility(const abstract_type& previous, bool (abstract_type::*predicate)(const abstract_type&) const) const;
    static sstring make_name(const std::vector<data_type>& types);
};

data_value make_tuple_value(data_type tuple_type, tuple_type_impl::native_type value);

class user_type_impl : public tuple_type_impl {
    using intern = type_interning_helper<user_type_impl, sstring, bytes, std::vector<bytes>, std::vector<data_type>>;
public:
    const sstring _keyspace;
    const bytes _name;
private:
    std::vector<bytes> _field_names;
    std::vector<sstring> _string_field_names;
public:
    using native_type = std::vector<data_value>;
    user_type_impl(sstring keyspace, bytes name, std::vector<bytes> field_names, std::vector<data_type> field_types)
            : tuple_type_impl(make_name(keyspace, name, field_names, field_types), field_types)
            , _keyspace(keyspace)
            , _name(name)
            , _field_names(field_names) {
        for (const auto& field_name : _field_names) {
            _string_field_names.emplace_back(utf8_type->to_string(field_name));
        }
    }
    static shared_ptr<const user_type_impl> get_instance(sstring keyspace, bytes name, std::vector<bytes> field_names, std::vector<data_type> field_types) {
        return intern::get_instance(std::move(keyspace), std::move(name), std::move(field_names), std::move(field_types));
    }
    data_type field_type(size_t i) const { return type(i); }
    const std::vector<data_type>& field_types() const { return _types; }
    bytes_view field_name(size_t i) const { return _field_names[i]; }
    sstring field_name_as_string(size_t i) const { return _string_field_names[i]; }
    const std::vector<bytes>& field_names() const { return _field_names; }
    sstring get_name_as_string() const;
    virtual shared_ptr<cql3::cql3_type> as_cql3_type() const override;
    virtual bool equals(const abstract_type& other) const override;
    virtual bool is_user_type() const override { return true; }
    virtual bool references_user_type(const sstring& keyspace, const bytes& name) const override;
    virtual std::experimental::optional<data_type> update_user_type(const shared_ptr<const user_type_impl> updated) const override;
private:
    static sstring make_name(sstring keyspace, bytes name, std::vector<bytes> field_names, std::vector<data_type> field_types);
};

data_value make_user_value(data_type tuple_type, user_type_impl::native_type value);

using user_type = shared_ptr<const user_type_impl>;
using tuple_type = shared_ptr<const tuple_type_impl>;

inline
data_value::data_value(std::experimental::optional<bytes> v)
        : data_value(v ? data_value(*v) : data_value::make_null(data_type_for<bytes>())) {
}

template <typename NativeType>
data_value::data_value(std::experimental::optional<NativeType> v)
        : data_value(v ? data_value(*v) : data_value::make_null(data_type_for<NativeType>())) {
}

template <typename NativeType>
data_value::data_value(const std::unordered_set<NativeType>& v)
    : data_value(new set_type_impl::native_type(v.begin(), v.end()), set_type_impl::get_instance(data_type_for<NativeType>(), true))
{}

template<>
struct appending_hash<data_type> {
    template<typename Hasher>
    void operator()(Hasher& h, const data_type& v) const {
        feed_hash(h, v->name());
    }
};

/*
 * Support for CAST(. AS .) functions.
 */

using castas_fctn = std::function<data_value(data_value)>;

castas_fctn get_castas_fctn(data_type to_type, data_type from_type);